American tegumentary leishmaniasis is a zoonotic endemic disease in Peru, caused by several Leishmania species and transmitted by sand fly vectors. There is an increased number of cases due to urbanization expansion and tourism. Clinical manifestations vary from chronic cutaneous ulcers (CL) to a delayed and metastasic infiltration of the upper airway mucosal membranes (ML). First line parenteral treatment with antimonials is toxic and is associated to treatment failure. Th1-type immunity plays a major role for parasite control in infected tissue. Despite clinical resolution, parasites are seldom eliminated completely. Parasite persistence is conditioned by T-regulatory cells (Tregs), a special subset of CD4+ lymphocytes, which express CD25 and FoxP3 as observed in murine models, where Tregs role in suppressing immunity against Leishmania infection has been well established. There are limited data in humans on the role of Tregs in CL and ML, which is the focus of this proposal. Our Institution has over 20 years of experience in the diagnosis and treatment of tegumentary leishmaniasis. We have recently standardized a flow cytometry technique to characterize tissue Tregs from human Leishmania infected tissue. We hypothesize that Tregs mediate parasite persistence in human Leishmania lesions and that late mucosal disease may develop as a consequence of the host inability to completely clear parasites. The specific aims for these proposal are: 1) to test the hypothesis that regulatory T-cells accumulate in Leishmania-infected tissue and dampen protective immune responses, 2) to test the hypothesis that Tregs are increased in numbers in mucosal leishmaniasis, providing evidence of their involvement in reactivated lesions and 3) to test the hypothesis that regulatory T-cells decrease in response to effective antimonial therapy and that treatment failure is associated with increased proportions or persistence of Tregs in tissues during cutaneous leishmaniasis. In accomplishing these goals, we will build a foundation for further studies of immune regulation in leishmaniasis, which is important for the development of immunotherapy and vaccines. We will build a team of outstanding Peruvian and foreign collaborators for further studies of the local immune responses in leishmaniasis. The long-range goals include development of immunologic reagents for therapy and prevention. PUBLIC HEALTH RELEVANCE: Human leishmaniasis is one of the most important parasitic diseases in the world. We plan to investigate the role of cells that suppress immunity during this infection. We believe the knowledge derived from this study will change significantly the concepts of this disease, opening new windows of research in treatment that may potentially benefit millions.